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757055ae8d
stdin, stdout, and stderr standard I/O stream are created for the init
process. They are not available when there is no console registered
for /dev/console. It might lead to a crash when the init process
tries to use them, see the commit 48021f9813 ("printk: handle
blank console arguments passed in.").
Normally, ttySX and ttyX consoles are used as a fallback when no consoles
are defined via the command line, device tree, or SPCR. But there
will be no console registered when an invalid console name is configured
or when the configured consoles do not exist on the system.
Users even try to avoid the console intentionally, for example,
by using console="" or console=null. It is used on production
systems where the serial port or terminal are not visible to
users. Pushing messages to these consoles would just unnecessary
slowdown the system.
Make sure that stdin, stdout, stderr, and /dev/console are always
available by a fallback to the existing ttynull driver. It has
been implemented for exactly this purpose but it was used only
when explicitly configured.
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20201111135450.11214-2-pmladek@suse.com
128 lines
2.8 KiB
C
128 lines
2.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2019 Axis Communications AB
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*
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* The console is useful for userspace applications which expect a console
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* device to work without modifications even when no console is available
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* or desired.
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*
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* In order to use this driver, you should redirect the console to this
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* TTY, or boot the kernel with console=ttynull.
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*
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* Based on ttyprintk.c:
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* Copyright (C) 2010 Samo Pogacnik
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*/
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#include <linux/console.h>
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#include <linux/module.h>
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#include <linux/tty.h>
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static const struct tty_port_operations ttynull_port_ops;
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static struct tty_driver *ttynull_driver;
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static struct tty_port ttynull_port;
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static int ttynull_open(struct tty_struct *tty, struct file *filp)
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{
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return tty_port_open(&ttynull_port, tty, filp);
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}
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static void ttynull_close(struct tty_struct *tty, struct file *filp)
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{
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tty_port_close(&ttynull_port, tty, filp);
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}
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static void ttynull_hangup(struct tty_struct *tty)
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{
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tty_port_hangup(&ttynull_port);
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}
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static int ttynull_write(struct tty_struct *tty, const unsigned char *buf,
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int count)
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{
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return count;
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}
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static int ttynull_write_room(struct tty_struct *tty)
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{
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return 65536;
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}
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static const struct tty_operations ttynull_ops = {
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.open = ttynull_open,
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.close = ttynull_close,
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.hangup = ttynull_hangup,
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.write = ttynull_write,
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.write_room = ttynull_write_room,
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};
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static struct tty_driver *ttynull_device(struct console *c, int *index)
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{
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*index = 0;
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return ttynull_driver;
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}
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static struct console ttynull_console = {
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.name = "ttynull",
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.device = ttynull_device,
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};
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void __init register_ttynull_console(void)
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{
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if (!ttynull_driver)
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return;
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if (add_preferred_console(ttynull_console.name, 0, NULL))
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return;
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register_console(&ttynull_console);
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}
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static int __init ttynull_init(void)
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{
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struct tty_driver *driver;
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int ret;
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driver = tty_alloc_driver(1,
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TTY_DRIVER_RESET_TERMIOS |
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TTY_DRIVER_REAL_RAW |
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TTY_DRIVER_UNNUMBERED_NODE);
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if (IS_ERR(driver))
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return PTR_ERR(driver);
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tty_port_init(&ttynull_port);
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ttynull_port.ops = &ttynull_port_ops;
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driver->driver_name = "ttynull";
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driver->name = "ttynull";
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driver->type = TTY_DRIVER_TYPE_CONSOLE;
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driver->init_termios = tty_std_termios;
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driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
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tty_set_operations(driver, &ttynull_ops);
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tty_port_link_device(&ttynull_port, driver, 0);
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ret = tty_register_driver(driver);
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if (ret < 0) {
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put_tty_driver(driver);
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tty_port_destroy(&ttynull_port);
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return ret;
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}
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ttynull_driver = driver;
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register_console(&ttynull_console);
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return 0;
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}
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static void __exit ttynull_exit(void)
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{
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unregister_console(&ttynull_console);
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tty_unregister_driver(ttynull_driver);
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put_tty_driver(ttynull_driver);
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tty_port_destroy(&ttynull_port);
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}
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module_init(ttynull_init);
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module_exit(ttynull_exit);
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MODULE_LICENSE("GPL v2");
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